Drive device for a piston in a container containing an injectable product

ABSTRACT

A drive arrangement for an injection device, including a first stage, a second stage and a drive for shifting the stages, wherein the drive acts on one of the stages to shift said one of the stages first and wherein the stage which is first shifted encounters a higher resistance than does the other stage, such that the other stage is shifted.

PRIORITY CLAIM

This application is a Continuation application of PCT/CH01/00155, filedon Mar. 13, 2001, which claims priority to German Patent Application No.DE 100 15 175.2, filed on Mar. 27, 2000, both of which are incorporatedherein by reference.

BACKGROUND

The invention relates to a drive for a piston in a container containingan injectable product.

Portable injection and/or infusion devices are used to administer forexample medicines in fluid form, in particular in liquid form, forexample insulin. The medicine fluid is displaced from a fluid containerby means of a piston and administered in precise doses.

Drive devices for the piston of the type which are preferred for thepurposes of the present invention are known from WO 98/47552. These aretelescopic drives, in which a first shifting stage shiftably mounted inor on a base part advances the piston in an advancing direction in thecontainer when it is itself advanced, displacing the product from thecontainer. In addition to the first shifting stage, at least a secondshifting stage is provided which can be shifted in the advancingdirection relative to the base part and which slaves the first shiftingstage in the advancing direction when it is shifted. The shifting stagesare shifted relative to the base part and to each other by spindledrives. By using a number of spindle drives, a long shifting path can beset precisely. However, thread pairings, such as those formed by spindledrives, exhibit axial play. The magnitude of the play is determined bythe thread tolerances.

SUMMARY

A object of the invention is to improve the precision of dosing amedicinal product, using an injection device or an portable infusiondevice.

In one embodiment, the present invention involves injection devices andcomprises a drive arrangement comprising a first stage, a second stageand a drive for shifting the stages, wherein the drive acts on one ofthe stages to shift said one of the stages first and wherein the stagewhich is first shifted encounters a higher resistance than does theother stage, such that the other stage is shifted.

The invention starts from the following recognition: after the producthas been completely delivered from the container, the shifting stagesare situated in a front position. From this front position, the shiftingstages are shifted back to a starting position and are ready for newproduct to be administered. In the starting position, the shiftingstages are each retracted against a fixed stopper or other suitable stopstructure. Those thread flanks of the spindle drives which form thedriving flanks during retraction are the driven flanks when the shiftingstages are extended. The driving flanks of each of the spindle drivesalternate between extending and retracting. Due to the thread play, thedriving threads during extension each have to complete a certainrotational movement before a driving flank of the driving thread pressesagainst a counter flank of the driven thread of the spindle drive andcauses the driven shifting stage to advance. If a shifting stage isadvanced from the starting position in the advancing direction, then arotational movement of a driving thread only generates an advancingmovement of said shifting stage when the play in the spindle drive hasbeen compensated for, i.e., when at least one driving flank of thedriving thread presses against a counter flank of the thread of thedriven shifting stage.

The conditions described above apply in principle before each firstextension following a complete or partial retraction. If a drive devicecomprises two or more shifting stages, and said two or more shiftingstages are to be extended for the first time after having beenretracted, then the shifting positions of said shifting stages are notdefined within the context of the thread play.

In accordance with the present invention, the shifting stage of at leasttwo shifting stages, which is advanced as the first of said two shiftingstages from a starting position by a pre-set shifting path length, isprevented from advancing further, beyond the pre-set shifting pathlength. It experiences, at least in sections, a higher resistanceagainst advancing further than does the other shifting stage, such thatthe other shifting stage is likewise advanced. The resistance cited isat least sufficiently large for the other shifting stage to be extendeda first time, i.e., it is larger than the unavoidable resistance whichhas to be overcome in order to extend the other shifting stage. Theincreased resistance can, however, be overcome by the drive. The pre-setshifting path length is non-zero, but is preferably selected to be assmall as possible. In any event, the shifting stage in question isadvanced some way under the influence of the spindle drive driving it,since in this case the thread play has definitely been compensated for.The pre-set shifting path length is preferably selected to be smallerthan the distance by which the piston has to be advanced when primed,despite the play having been compensated for, when the parts of theadministering device which guide the product are to be vented. The playin the spindle drives is thus already compensated for as the device foradministering the product is primed.

In one embodiment, the present invention comprises a drive arrangementfor an injection device, the drive arrangement comprising a firstshifting stage, a second shifting stage which, when shifted, slaves thefirst shifting stage, wherein the first shifting stage may be shiftedrelative to the second shifting stage and the first and second shiftingstages at least partially overlap, and a drive for shifting the shiftingstages, wherein the drive acts on one of the shifting stages via a firstspindle drive and wherein a second spindle drive is formed between theshifting stages, and further wherein the shifting stage which is firstshifted encounters a higher resistance than does the other shiftingstage, such that the other shifting stage is shifted.

The shifting stage which extends as the first of the shifting stagesfrom the starting position can be clearly determined in advance usingconstructive measures. For instance, the thread frictions of the twospindle drives can be selected differently, for example by selectingappropriate materials. Instead or in addition, the shifting stage whichis not to be advanced as the first can persist in its starting positiondue to a slight pressing fit, as long as the shifting stage which ispredetermined in this way as the first to be advanced has not yetexperienced the increased resistance. As soon as the increasedresistance has been established, the shifting stage is released from itspressing fit and is then advanced. In order to obtain resistances ofdifferent magnitudes against the first extension, the mesh lengths ofthe threads of the two spindle drives during full mesh or only in thestarting position of the shifting stages can also be selected so as tobe of different magnitudes. The shifting stage which is driven by thespindle drive with the shorter thread mesh, at least in the startingposition, extends as the first shifting stage and experiences the higherresistance, at least in sections, once the pre-set path length has beencovered.

The higher resistance, at least in sections, can be generated by formingan advancing brake acting between the shifting stage which advances asthe first shifting stage and the other shifting stage or another bodyrelative to which the shifting stage which advances first may be shiftedin the advancing direction. The other body can be non-shiftablyconnected to the base part or formed by the base part itself.

In some preferred embodiments, a resistance area is formed on a surfacearea of the shifting stage which advances first, and a resistancecounter area is formed on a surface area relative to which the shiftingstage which advances first may be shifted in the advancing direction.The higher resistance, at least in sections, is generated by a pressureexerted by the resistance area onto the resistance counter area. Theresistance area and the resistance counter area form a advancing brake,either on their own or in co-operation with a resistance element or anumber of resistance elements.

The advancing brake can be based solely on sliding friction. Anincreased sliding friction in sections can be obtained by forming eachof the resistance area and the resistance counter area as a narrow stripin the advancing direction. The roughness of the resistance area and theroughness of the resistance counter area are such that a resistance isgenerated when these two areas slide over one another, said resistanceensuring that the shifting stage which advances first is fixed and theat least one other shifting stage is advanced, but wherein saidresistance can on the other hand be easily overcome by driving the drivedevice.

The resistance area and the resistance counter area are advantageouslyformed by a collar formed on each of the surface areas in question. Thecollars can each be formed by a radial protrusion or bulge. Thisprotrusion or bulge can be flexible, such that the collar formed by itgives under a pressure exerted by the other collar, but still does notexpose the path, in order to firstly generate the higher resistance inaccordance with the invention. In some embodiments, the resistance areaand the resistance counter area can both be flexible. In someembodiments, the radial protrusion or bulge is preferably formed to runor extend around the whole circumference. In sections, it reduces aradial distance formed between the shifting stage in question and thesurface area facing it.

In one preferred embodiment, a resistance element is arranged betweenthe resistance area and the resistance counter area, the resistance areaexerting the pressure force onto the resistance counter area via saidresistance element. If said resistance element is flexible, as in somepreferred embodiments, the resistance area and the resistance counterarea can be non-flexible. The resistance element gives under thepressure force, or suction force as the case may be, of the shiftingstage which advances first. It offers resistance to said shifting stageadvancing further, which preferably increases with the degree offlexing.

In some preferred embodiments, the resistance element is elasticallyflexible. It is formed as a spring element which exerts an axial forceonto the shifting stage, counter to the advancing direction, when theshifting stage tenses the spring element. A spiral spring can, forexample, be provided, which is integrated in the drive deviceperpendicular to the advancing direction of the shifting stage. Thespiral spring exerts a resistance force onto the shifting stage, againstthe advancing direction, when it is ejected at its exposed end. Thespiral spring can be held on the shifting stage or on a surface areafacing it, relative to which the shifting stage can be shifted.

In some embodiments, the resistance against the shifting stage advancingis only increased in a partial region of the advancing path. Only onepoint on the shifting path of the shifting stage is needed at which theresistance of said shifting stage is increased relative to the othershifting stage. The shifting stage which experiences a higher resistanceremains at this point until an even greater resistance opposes the othershifting stage. At the latest, this is the case when the other shiftingstage has reached its maximum extending length. The shifting stage whichis braked or stopped first is then moved beyond the region in which anincreased resistance counteracts it, and subsequently movesonwards—preferably again under low resistance—as far as the point ofmaximum shifting, i.e., minimum overlap between the shifting stages.

In one preferred embodiment, the resistance element is formed by anO-ring, which may be made of plastic. A spring-elastic element, such as,for example, an annular spring made of metal or plastic, or an annularspiral spring, can also be used.

In one preferred embodiment, the resistance element is formed by anelastically flexible clip. The clip protrudes into the shifting path ofthe shifting stage which advances first and is ejected by the advancingshifting stage. The clip can instead also be attached to the shiftingstage and push against a collar on the surface area facing it.

In some embodiments, an advancing brake is preferably provided for eachof the shifting stages. Each of the number of advancing brakes may beformed like one of the embodiments described above.

In one preferred embodiment, a single flexible resistance element isused for the first and the second shifting stage. This common resistanceelement is preferably non-shiftably connected to one of the shiftingstages or to the base part.

The at least two shifting stages can only be definitively extendedwithout a separate advancing brake, using only the threads of thespindle drives. In this embodiment, the spindle drives are purposefullyproduced with different thread frictions per convolution, i.e., withdifferent specific thread frictions. The shifting stage which advancesfirst is driven by a spindle drive with the greater specific threadfriction. However, the thread mesh of this spindle drive is shorter, inthe starting position of the shifting stage which it drives, than thethread mesh of the other spindle drive in the starting position of theother shifting stage. The lengths of the two thread meshes in thestarting position are selected such that smaller friction forces occur,despite the greater thread friction in the one spindle drive, due to thesmaller thread mesh in the starting position. In this way, the shiftingstage driven by this spindle drive is determined in advance as theshifting stage which advances first. As the thread mesh increases inlength, however, the frictional resistance increases, until it exceedsthe frictional resistance of the other spindle drive. At the latest,this state results when there is full thread mesh in the spindle drivewith the greater specific thread friction. Special high-friction brakingzones can also be provided in the threads at appropriate points.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 depicts a drive device for a piston of an infusion device, in itsstarting position;

FIG. 2 is a more detailed view of area “R” from FIG. 1, depictingO-rings as resistance elements;

FIG. 3 is a more detailed view of area “R” an infusion device derivedfrom FIG. 1, depicting a single resistance element in the form of anelastically flexible clip;

FIG. 4 depicts the resistance element of FIG. 3; and

FIG. 5 depicts a modification of the resistance element of FIGS. 3 and4.

DETAILED DESCRIPTION

FIG. 1 shows a longitudinal section through a drive device. The drivedevice comprises as its main components: a base part 1; two shiftingstages 10 and 20 which can be linearly shifted relative to the base part1; and an axially fixed rotary drive member 30 which is rotary mountedin the base part 1 and forms the drive. The first shifting stage 10 isformed as a threaded rod comprising an external thread 10 a. The secondshifting stage 20 is a threaded sleeve comprising an internal thread 20i and an external thread 20 a. The rotary drive member 30 is a hollowcylinder and will be referred to herein as the drive 30. The drive 30comprises an internal thread 30 i on a head region and a slavingtoothing 31 on a foot region, by which the drive 30 is driven by amotor.

The threaded sleeve 20 and the drive 30 form a first spindle drive viatheir threads 20 a and 30 i. The threaded rod 10 and the threaded sleeve20 form a second spindle drive via their threads 10 a and 20 i. The twosleeves 20 and 30 surround the threaded rod 10 concentrically with acommon central longitudinal axis which simultaneously lies in theadvancing direction of the drive device. The drive device shifts apiston, which is accommodated in a reservoir or container containing amedicine fluid, in this advancing direction when the shifting stages areadvanced, in that the threaded rod 10—as the foremost or first shiftingstage, pressing against the piston via a front plunger 13—advances saidpiston towards an outlet of the container and thus displaces liquid fromthe container. The base part 1 fixes the drive device relative to thecontainer. The base part 1 can be attached to a casing accommodating thecontainer or can be formed by a casing of an injection and/or infusiondevice. In such a casing, the base part is preferably mounted floatingand may be linearly shifted in the advancing direction.

A rotational movement of the drive sleeve 30 is transmitted onto thethreaded sleeve 20 via the first spindle drive formed between thethreads 20 a, 30 i. Depending on the frictional forces acting on thethreaded sleeve 20, the threaded sleeve 20 is either rotationally slavedor shifted along its rotational axis by the first spindle drivecomprising the threads 20 a, 30 i. The movement of the threaded sleeve20 can also be a composite shifting and rotational movement. Thethreaded sleeve 20 simply slaves the threaded rod 10 as far as it isshifted. Where the threaded sleeve 20 is rotated, the rotationalmovement of the threaded sleeve 20 generates an advancing movement ofthe threaded rod 10 relative to the threaded sleeve 20 via the secondspindle drive formed by the threads 10 a and 20 i, as a result of arotational block 40 on the threaded rod 10. In some embodiments, thespindle drives of the two shifting stages 10 and 20 are preferably eachin the same direction.

FIG. 1 shows the drive device in a starting position. In the startingposition, the overlapping shifting stages 10 and 20 are accommodated ina hollow space of the base part 1 and the drive 30. The shifting stages10 and 20 are retracted up to a stopper, such that they maximallyoverlap.

FIG. 2 shows a detail of the drive device. An O-ring 2 is accommodatedin an annular groove 11 in the foot region of the first shifting stage10. The O-ring 2 can be a conventional sealing ring. A further O-ring 2is accommodated in an outer annular groove 21 of the second shiftingstage 20. An axially extending intermediate space 5 is formed betweenthe shifting stages 10, 20 and between the shifting stage 20 and thedrive 30; each of the O-rings 2 or another flexible element can beshifted, substantially freely, in said intermediate space 5. The O-rings2 are pressed together in constrictions 3 in the intermediate space 5.The O-rings 2 form bearings for the shifting stages. The respectivespindle drives form the second bearings. Each of the O-rings 2 is aflexible element which is pressed by the respective shifting stage inthe advancing direction, against a corresponding radial protrusion 3.The protrusions 3 protrude perpendicular to the advancing direction ofthe shifting stages 10, 20, into the respective shifting path of theO-rings. A radial protrusion 3 is formed circumferentially on an innersurface area of the second shifting stage 20. Another radial protrusion3 is circumferentially formed on an inner surface area of the drive 30.In the starting position of the drive device, the O-rings are eachsituated a pre-set shifting path length S10 or S20 in front of theradial protrusions 3 facing opposite them. The pre-set shifting pathlengths S10, S20 can be the same. The shifting path lengths are pre-setby the position of the annular grooves 11 and 21.

If the O-rings 2 are held in their receptacles 11, 21 with play, thisplay can be added to the shifting path lengths.

In one embodiment, a resistance area 12 is formed by a rear limitingarea of the groove 11. When the first shifting stage 10 is advancedrelative to the second shifting stage 20, the resistance area 12presses, indirectly via the O-ring, against a resistance counter area23. The resistance counter area 23 is provided on the inner surface areaof the second shifting stage 20. It is formed by the protrusion 3. Whenthe first shifting stage 10 is advanced relative to the second shiftingstage 20, the O-ring 2 between the resistance area 12 and the resistancecounter area 23 is pressed together.

Correspondingly, a rear limiting area of the groove 21 forms aresistance area 22. The resistance area 22 presses via the other O-ring2 onto a resistance counter area 31 formed by the protrusion 3 of thedrive 30, and thus in the same way generates a higher resistance beforepassing the constriction.

Proceeding from the starting position described above, a first deliverytakes place. Depending on the frictional conditions of the shiftingstages 10 and 20, which follow from the internal friction of the spindledrives and the friction of the shifting stage bearings, either there isa relative movement in the first spindle drive, comprising threads 20 a,30 i, such that the second shifting stage 20 is advanced first, or thereis a relative movement in the second spindle drive, comprising threads10 a, 20 i, such that the first shifting stage 10 is advanced first,relative to the base part and the second shifting stage. The shiftingstage to which a lesser resistance against advancing is offered begins ashifting movement or is advanced more quickly. At the beginning of therelative movement in the corresponding spindle drive, the thread play ofthe spindle drive in the advancing direction is first compensated for,and then the shifting stage is advanced.

The respective pre-set shifting path length S10 or S20, by which ashifting stage is advanced before it experiences a higher resistance, atleast in sections, against shifting further than does the other shiftingstage, can be different for each shifting stage. The pre-set shiftingpath lengths S10, S20 are preferably selected so as to be as small aspossible. They do not have to be adjusted to the play of the spindledrive. Preferably, they are adjusted to the distance by which the pistonis advanced when primed. A sum of the pre-set shifting path lengths S10,S20 should be at most as large as the shifting path of the piston whenthe device is primed. Since each of the shifting stages 10, 20 isbraked, at least in sections or at intervals, in accordance with theshifting path length S10, S20 set for it, which of the two shiftingstages 10, 20 is advanced first is irrelevant for compensating for theplay in the two spindle drives.

FIG. 3 shows a drive device in accordance with FIG. 1, with thedifference that a common flexible element 2 is used for the two shiftingstages 10, 20. The flexible element 2 is held in an annular groove 24running around an outer surface area of the second shifting stage 20.The flexible element 2 is embodied as a rotating body made of a flexiblematerial, preferably plastic. It comprises two elastically, flexiblymoving clips 4.10, 4.30. A first clip 4.10 projects towards the firstshifting stage 10, while the second clip 4.30 projects towards the drive30 on the other side. At the rear end of the first shifting stage 10, aradial bulged protrusion 3.10 is formed which presses against the clip4.10 of the flexible element 2 when the shifting stage 10 is shifted inthe advancing direction relative to the shifting stage 20. When thesecond shifting stage 20 is advanced relative to the drive 30, the clip4.30 is pressed against a radial bulge 3.30 of the drive 30. As in thepreviously described embodiment, a resistance area 12 or 22 pressesfirst onto a resistance counter area 23 or 31 via a flexible resistanceelement 4.10 or 4.30. The resistance counter area 23 for the resistancearea 12 is formed by a rear facing area of the second shifting stage 20.As in the previously described embodiment, the play in both spindledrives is compensated for at the beginning of the advancing movements ofthe two shifting stages 10, 20.

FIG. 4 shows the common flexible element 2 in accordance with FIG. 3,individually. The element preferably consists of one part. It could,however, also be composed of a number of components. The clips 4.10,4.30 are closed in a circle. In order to brake the shifting stages, theclip 4.10 is pressed radially outwards and the clip 4.30 radiallyinwards. It is also possible to provide the resistance element or justthe clips 4.10 and/or 4.30 with longitudinal slits or axial recesses.The flexible element 2 comprises a groove-shaped recess 6 on its innersurface area. A rear rim area 7 of this recess 6 is pressed against theresistance counter area 23 when the shifting stage 10 is first advancedrelative to the shifting stage 20. A front rim area 8 serves to positionthe resistance area 22 against the flexible element 2.

One example, in which the clips 4.10, 4.30 are only formed at individualsegments of the circumference, may be seen in FIG. 5. The clips 4.10,4.30 do not extend around the entire circumference. A center part 5 isgiven an annular form and connects the clips 4.30 to the clips 4.10. Inthe example depicts, four clips 4.10 and four clips 4.30 are eacharranged evenly distributed around the circumference. Attaching hooks 9,likewise evenly distributed over the circumference, are provided, viawhich the flexible resistance element is axially attached in the annulargroove 24 of the second shifting stage 20. They are arranged laterallyoffset with respect to the clips 4. This improves a slight mobility ofthe clips 4 in the radial direction. The increased resistance offered toa shifting stage when a radial protrusion presses against the clips4.10, 4.30 in the axial direction is determined by the elasticity of theclips. This is dependent on the material used for the clips and on theshape of the clips. If a larger circumferential region is covered, thenthe force required to eject the clips increases generally.

In the foregoing description, embodiments of the invention, includingpreferred embodiments, have been presented for the purpose ofillustration and description. They are not intended to be exhaustive orto limit the invention to the precise form disclosed. Modifications orvariations are possible in light of the above teachings. The embodimentswere chosen and described to provide the best illustration of theprincipals of the invention and its practical application, and to enableone of ordinary skill in the art to utilize the invention in variousembodiments and with various modifications as are suited to theparticular use contemplated. All such modifications and variations arewithin the scope of the invention as determined by the appended claimswhen interpreted in accordance with the breadth they are fairly,legally, and equitably entitled.

The invention claimed is:
 1. A drive device for a piston in a containercontaining an injectable product, said drive device comprising: a) afirst shifting stage which may be shifted relative to a base part from astarting position and which, when shifted in an advancing direction,advances said piston in said container, displacing product from saidcontainer in doses; b) at least a second shifting stage which may beshifted in said advancing direction relative to said base part from astarting position and which, when shifted in said advancing direction,slaves said first shifting stage; c) wherein said first shifting stagemay be shifted in said advancing direction relative to said secondshifting stage, and said first shifting stage and said second shiftingstage at least partially overlap, viewed in said advancing direction; d)and a drive for advancing said shifting stages; e) wherein said driveacts on one of said shifting stages via a first spindle drive; f) andwherein a second spindle drive is formed between said shifting stages;wherein: g) proceeding from said starting position of said shiftingstages, said shifting stage which is first advanced by a pre-setshifting path length experiences a higher resistance, at least insections, against possibly shifting even further than does the other ofthe shifting stages, such that said other shifting stage is likewiseadvanced, wherein said higher resistance is can be overcome by the drivedevice such that said shifting stage that is first advanced is advancedfurther in the advancing direction after overcoming the higherresistance.
 2. The drive device as set forth in claim 1, wherein saidhigher resistance is generated by a flexible resistance element againstwhich said shifting stage which is advanced first presses once it hascovered said pre-set path length.
 3. The drive device as set forth inclaim 2, wherein said resistance element is elastically flexible.
 4. Thedrive device as set forth in claim 2, wherein said resistance element isformed by an O-ring.
 5. The drive device as set forth in claim 2,wherein said resistance element is formed by a flexibly moving clip. 6.The drive device as set forth in claim 2, wherein each of said shiftingstages, once it has been advanced by said respective path length, ispressed against a flexible resistance element when advanced further. 7.The drive device as set forth in claim 6, wherein a common flexibleresistance element is provided for said shifting stages.
 8. The drivedevice as set forth in claim 1, wherein: a resistance area is formed ona surface area of said first shifting stage; a resistance counter areais formed on a surface area with respect to which said first shiftingstage may be shifted in said advancing direction; and said higherresistance is generated by a pressure exerted onto said resistancecounter area by said resistance area.
 9. The drive device as set forthin claim 8, wherein a flexible resistance element is arranged betweensaid resistance area and said resistance counter area.
 10. The drivedevice as set forth in claim 8, wherein said resistance area is formedby a collar and said resistance counter area is formed by a countercollar facing said collar.
 11. The drive device as set forth in claim 1,wherein: a resistance area is formed on a surface area of said secondshifting stage; a resistance counter area is formed on a surface areawith respect to which said second shifting stage may be shifted in saidadvancing direction; and said higher resistance is generated by apressure exerted onto said resistance counter area by said resistancearea.
 12. The drive device as set forth in claim 11, wherein a flexibleresistance element is arranged between said resistance area and saidresistance counter area.
 13. The drive device as set forth in claim 11,wherein said resistance area is formed by a collar and said resistancecounter area is formed by a counter collar facing said collar.
 14. Thedrive device as set forth in claim 1, wherein said spindle drives areprovided with frictional resistances of different magnitudes.
 15. Thedrive device as set forth in claim 1, wherein said pre-set shifting pathlength is shorter than a distance by which the piston is advanced duringa priming movement.
 16. A drive arrangement for an injection device,including a first stage, a second stage and a drive for shifting thestages, wherein the drive acts on one of the stages to shift said one ofthe stages first, wherein the stage which is shifted first encounters ahigher resistance than does the other stage, such that the other stageis shifted, and wherein said higher resistance is overcome by the drivesuch that said shifting stage that is first shifted is shifted furtherafter overcoming the higher resistance.
 17. The drive arrangementaccording to claim 16, wherein the stages at least partially overlap andthe first stage may be shifted relative to the second stage.
 18. Thedrive arrangement according to claim 16, wherein the drive acts on saidone of the stages via a first spindle drive and wherein a second spindledrive is formed between the stages.